1. Field of the Invention
The present invention relates to a paint masking tape, and more particularly to a paint masking tape that does not tear or scatter paint flakes easily when peeled off.
2. Description of the Related Art
The paint masking tapes widely used in the painting of vehicles or buildings are commonly configured in such a way that an adhesive layer for pasting the masking tape to the paint object is formed on one side of a tape substrate such as a plastic film (polyolefin film, polyester film, or the like) or paper.
A paint masking tape must provide clearly visible "parting lines" (border lines between painted areas and unpainted areas, or border lines between areas painted in different colors). A paint masking tape must also be easy to handle and must not tear readily or cause flaking (a phenomenon in which the coat of paint on the tape separates in flakes from the tape substrate during tape removal) when peeled off, contaminating the painted surface.
A technique in which a resin layer is formed in order to inhibit or otherwise affect flaking on the adhesive-free surface of the tape substrate of a paint masking tape (on the back surface of the substrate) has been widely used in the past in order to meet such requirements.
For example, Japanese Patent Application Laid-Open No. 2-247272 describes a paint masking tape obtained by applying and forming a chlorinated polyolefin film on the back surface of a polyolefin film substrate, and has a statement that the chlorinated polyolefin film improves adhesion between the tape surface and the paint coat, preventing flaking in which the resulting paint flakes are peeled off and scattered, and making it possible to prevent the paint surface from being contaminated.
In addition, Japanese Patent Application Laid-Open No. 7-82536 describes a paint masking tape obtained by applying and forming a specific vinyl copolymer film on the back surface of a paper substrate, and has a statement that the specific vinyl copolymer film imparts flexibility to the entire paint masking tape, preventing the tape from being fragmented when it is peeled off, and making parting lines on curved portions clearly visible.
A disadvantage of this approach, however, is that when the paint masking tapes described in the aforementioned publications are actually used during the surface painting of vehicles, these tapes easily tear during their removal.
The inventors have conducted a detailed study into the reasons for this phenomenon and found that the paints used for the surface painting of vehicles are usually so-called baking paints, which possess thermosetting properties and form extremely hard and brittle paint films when baked. Specifically, separating a paint masking tape from a painted surface (painted object) facilitates tape tearing because the masking tape and the paint film are firmly bonded and integrated, and the hardness and brittleness of the paint film in a laminate composed of a masking tape and a paint film remain dominant even when the tape substrate is rendered highly flexible. In the particular case of a paint object with a complicated or curved shape, it is very difficult even for an experienced person to peel off the tape without tearing it.
To address such tape tearing problems of paint masking tapes, it has been proposed to reduce the adhesion between the paint masking tapes and paint films, but this approach is disadvantageous in that the paint films separate from the tape substrate and scatter in the form of flakes, contaminating the paint surface, during peeling operations. In addition, parting lines are often rendered indistinguishable when such paint flakes are formed.